The annual July survey of bighorn sheep in Anza-Borrego Desert State Park netted the second-largest count in 41 years, leaders said Tuesday.

Under the guidance of state parks officials, volunteers endured searing heat to tally 329 Peninsular bighorn sheep in the park during from July 1-3. The total was a huge jump from last year, when 255 sheep were spotted, but short of the record 356 sheep detected in 2009.

The Anza-Borrego Foundation, a non-profit advocacy group that finances the census, said all the volunteers made it out safely.

"It's pretty intense," said Gary Katz, a spokesman for the foundation. "They are sheep aficionados, what can I say? For most people, it's a passion for the desert. It's an extreme environment that you can go into and know that you have the backup from the rangers."

Peninsular bighorn sheep

Habitat: Steep slopes, canyons and washes in desert regions

Diet: Acacia, encelia, sweetbush and other desert plants

Range: Parts of Baja California and the Peninsular Ranges of San Diego, Imperial and Riverside counties, including the San Jacinto, Santa Rosa, Vallecito and In-Ko-Pah mountains

Combined with data from helicopter surveys, the count suggests the sheep population continues to rebound from lows in the mid-1990s, said Mark Jorgensen, a former superintendent of the state park who has attend all but a handful of the annual surveys.

"We're very satisfied," he said. "There are healthy numbers of animals out there."

Peninsular bighorns are federally protected because their numbers shriveled in the 1980s and 1990s as development, disease and mountain lions reduced their numbers. By the late 1990s, fewer than 300 were thought to roam between Mount San Jacinto and the U.S.-Mexico border.

Once the Southern California population of the bighorn was protected under the Endangered Species Act in 1998, its fortunes started to turn. A conservation group has raised or rehabilitated more than 100 of the animals for release into the wild, and land managers removed livestock from parts of the bighorn sheep's range to control the spread of diseases.

The annual Anza-Borrego count just looks at a slice of the sheep's habitat in the state park, where volunteers watched watering holes 10 hours a day. About 45 of them endured daytime high temperatures from 103 to 116 for the chance to count sheep. Many of them hiked two or three hours into their locations and camped for three nights.

The most rams -- 23 -- were seen at Middle Spring-Tubb Canyon and the largest number of sheep overall -- 84 -- were seen at Rattlesnake Spring.

Census work is done in July because extreme heat drives sheep to water sources where they can be easily spotted.

"In December and January, they are scattered all over hundreds of thousands of acres in such a scenario that volunteers probably couldn't find them most of the time," Jorgensen said.

He said this year's crew of helpers came from several states, including Maryland. "It's refreshing to know that people will give up their Fourth of July weekend," he said. "They know they are part of good citizen science and they are working for something that they really love."